This invention refers to a gripping device for gripping and transporting sheets in single or multicolor silk screen printing machines, and in particular is directed to a gripper for conveying sheets in silk-screen printing machines of the type in which the gripper is supported by carriages and moved along a printing surface above silk-screen printing panels, to bring the individual sheets to be printed in line with the various work stations.
A gripper of the type referred to, in general comprises an elongated bar provided with gripping jaws which can be opened to allow the insertion of a sheet to be printed, and the removal of a printed sheet, and closed to retain a sheet. The gripper is normally supported at both ends by carriages connected to driving chains which run along lateral guides of the printing machine.
Grippers for printing machines are shown for example in U.S. Pat. No. 2.984.178, U.S. Pat. No. 3.924.849 and U.S. Pat. No. 4.526.100.
Grippers of this kind present several drawbacks and prove to be somewhat unsuitable in that they do not always allow to properly grip the sheets, and in addition tend to generate high gripping forces which are liable to pierce or damage the gripped sheet.
In order to partially obviate these drawbacks, U.S. Pat. No. 4.526.100 proposes a gripper device comprising a box-like supporting body provided with a flat jaw and a plurality of plate-like gripper elements set in mutual alignment for oscillation in respect to said juxtaposed flat jaw, by means of sliding elements which are reciprocated by a drive shaft of the silk screen printing machine. A gripper of this kind presents extremely complex structure and configuration, which will tend to generate excessively high gripping forces, which in certain cases may even piercing and damage the sheets.
The main object of this invention is to provide a gripper for conveying sheets in silk-screen printing machines, which is of innovative design and such as to obviate the aforementioned drawbacks.
In particular, one object of this invention is to provide a gripper of the above-mentioned type, which provides a wide contact surface for gripping the sheets, thereby reducing the specific contact pressures.
A still further object of this invention is to provide a gripper as mentioned above, which is extremely simple in design and can be manufactured from an extruded structural section with extremely inexpensive costs.
The above can be achieved by means of a gripping device for gripping and conveying sheets in single and multicolor silk-screen printing machines, comprising:
a box-like gripping bar having an upwardly and outwardly slanted rear wall provided with a longitudinally extending stepped edge having an upper sheet-gripping surface;
a plurality of side by side arranged plate-like gripping members, hingedly connected to the gripping bar to define a flat jaw;
preloaded spring members to bias each of said gripping members against the sheet gripping surface of said stepped edge of the gripping bar;
a plurality of lifting arms for said plate-like gripping members, operatively connected to a reciprocating drive shaft;
an actuating lever at each end of the drive shaft, to reciprocate the same and tiltably move said gripping members for gripping and releasing a sheet; and
carriage means at each end of box-like to run the gripping device along slide guides of the printing machine.